Proceedings of the International Cyanide Detection Testing Workshop

Philippines 2000) obtained at a Live Food
Fish Trade meeting held in Hong Kong in
2000 that only partially described the actual
SOP used by IMA. No attempt was made by
either Ms. Mak or Dr. Renneberg to contact
IMA to obtain the correct SOP manual.
The assertion by Mak et al (2005b) that
“The refl ux distillation method together
with an ISE was not sensitive enough for
the determination of cyanide traces in postcyanide
exposed fi sh” is incorrect (Rubec
2007). Since, this was associated with a
discussion of the methods used by the IMA,
the implication was that the IMA could not
reliably measure cyanide concentrations
below 0.26 mg/L. However, Mak (2003) did
not use the same ISE equipment used by the
IMA. She used a Pheonix ISE electrode (Cat
No. CN01503); connected to a Jenway pH/
mV meter (model 3305); which has a range
of detection on a linear semi-log plot of
0.26 to 260 ppm (mg/L). The IMA used a
Thermo-Orion ISE electrode (#9406BN)
that can reliably detect cyanide concentrations
down to 0.03 mg/L on a linear semi-log plot
(ASTM 1997). Likewise, the pH/ISE meter
used by Mak (2003) differs from that used by
the BFAR/IMA laboratories (Thermo-Orion
Model 920A) (Manipula 1995, Manipula et
al.2001c).
The Thermo Orion ISE equipment (ISE
electrodes and meter) is capable of detecting
cyanide ion in solution with a straight-line
calibration on a semi-log plot down to 0.02
mg/L (2 ppb) (Frant et al. 1972; Orion
Research Inc. 1975, 1997; Sekerka and
Lechner 1976). This was routinely done with
daily calibrations conducted by the IMA
laboratories using the Thermo Orion ISE
equipment (Manipula et al. 2001c). This is
similar to round-robin fi ndings by the ASTM
(1987).
52
Mak et al. (2005b) reported that the lower
range of detection for cyanide ion using a
colorimetric method was 0.026 ppm. Hence,
they claimed that the colorimetric method
had a higher sensitivity than the ISE method
(actually both have about the same lower limit
of detection). They claimed that the cyanide
refl ux distillation method together with the ISE
was not sensitive enough for the determination
of traces in post-cyanide exposed fi sh. A series
of QA/QC experiments were conducted that
are irrelevant considering that the wrong ISE
equipment was utilized (Mak 2003). Mak et al.
(2005b) mistakenly concluded: “The cyanide
distillation method combined with the ISE
described in the SOP manual and employed
by the IMA laboratories requires considerable
modifi cation and elaboration. A reliable and
ultra sensitive system for cyanide detection
in fi sh is urgently needed.” It should also be
noted that the lower limit of detection for
the biosensor method that Mak et al. (2005c)
developed is 0.0286 ppm (mg/L), which is
about the same as the Thermo Orion ISE
method on a linear calibration (Sekerka and
Lechner 1976). Hence, it is not more sensitive
than the ISE method (ASTM 1997).
The present authors, including Dr. Kobelski
and Dr. Logue, believe that the ISE method
associated with the SOP manual used by the
IMA (Manipula 1995) and by the various
agencies that also use the method (including
APHA, ASTM, US-EPA and BFAR) is
scientifi cally reliable, although this has not been
demonstrated with fi sh tissue in controlled
experiments. This is also the opinion of Dr.
Ellen Gonter who helped develop the ISE
method for ASTM, Dr. Martin Frant of
Thermo Orion who developed the cyanide
ISE electrode, and Dr. George Dixon, an
expert concerning cyanide physiology in fi sh
and Vice-Dean of Research at the University
of Waterloo, Canada (all three provided letters